[PB] Do not show snapshot if uiMode has changed.

- Record uiMode in TaskSnapshot.
- While preparing predictive back animation, if the uiMode of snapshot
is not match activity's uiMode, fallback to use splash screen surface.
- Draw windowless splash screen with latest theme & configuration.

Flag: EXEMPT bugfix
Bug: 351119448
Test: follow issue description, switch dark/light theme then trigger
predictive back, verify no serious contrast changes.
Test: atest SnapshotDrawerUtilsTest StartingSurfaceDrawerTests
ActivityTaskManagerThumbnailLoaderTest ActivitySnapshotControllerTests
TaskSnapshotPersisterLoaderTest

Change-Id: I8c3b4e9444e5cfacf21c97da3b0d13c1ef76fcf3